There is shown in FIG. 1 a vertical cross sectional view of a conventional head drum assembly for use in a video cassette recorder.
The head drum assembly includes a stationary drum 101, a rotary shaft 102 rotatably fitted into the stationary drum 101, a rotary drum 103 closely fitted onto a top part of the rotary shaft 102 above the stationary drum 101, a motor 104 disposed under the stationary drum 101, for rotating the rotary shaft 102, and an upper and a lower bearings 105,106 fitted into the stationary drum 101, for rotatably supporting the rotary shaft 102 and the rotary drum 103 relative to the stationary drum 101. The bearings 105,106 are of an self-lubricated type, containing an oil lubricant impregnated during the manufacture thereof. An inner peripheral surface of the upper bearing 105 facing the rotary shaft 102 functions a radial bearing surface and a top surface thereof facing the rotary drum 103 functions a thrust bearing surface. When the rotary shaft 102 rotates, the impregnated oil tends to seep out, retained in a building-up groove formed on the thrust bearing surface and form an oil film between the bearing surfaces and surfaces of the rotary shaft 102 and the rotary drum 103 facing the bearing surfaces, to reduce the friction therebetween.
When the rotary drum rotates, however, part of the oil retained in the building-up groove may fly off as a result of rotation of the rotary drum, thereby preventing a sufficient amount of the oil to be retained in the building-up groove thereof for forming the oil film, preventing the rotary drum to rotate smoothly.